Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641

Abstract

Signs of damping wing absorption attenuating the Lyman-$\alpha$ emission line of the first known $z\sim 7$ quasar, ULAS J1120+0641, recently provided exciting evidence of a significantly neutral IGM. This long-awaited signature of reionization was inferred, in part, from a deficit of flux in the quasar's Lyman-$\alpha$ emission line based on predictions from a composite of lower-redshift quasars. The composite sample was chosen based on its C IV emission line properties; however, as the original study by Mortlock et al. noted, the composite contained a slight velocity offset in C IV compared to ULAS J1120+0641. Here we test whether this offset may be related to the predicted strength of the Lyman-$\alpha$ emission line. We confirm the significant ($\sim 10$ per cent at r.m.s.) scatter in Lyman-$\alpha$ flux for quasars of a given C IV velocity and equivalent width found by Mortlock et al. We further find that among lower-redshift objects chosen to more closely match the C IV properties of ULAS J1120+0641, its Lyman-$\alpha$ emission falls within the observed distribution of fluxes. Among lower-redshift quasars chosen to more closely match in C IV velocity and equivalent width, we find that ULAS J1120+0641 falls within the observed distribution of Lyman-$\alpha$ emission line strengths. This suggests that damping wing absorption may not be present, potentially weakening the case for neutral gas around this object. Larger samples of z$>$7 quasars may therefore be needed to establish a clearer picture of the IGM neutral fraction at these redshifts.

7 pages, 6 figures

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• XQR-30: the ultimate XSHOOTER quasar sample at the reionization epoch
• New Constraints on Quasar Evolution: Broad Line Velocity Shifts over $1.5\lesssim z\lesssim 7.5$
• A comparison of quasar emission reconstruction techniques for $z\ge 5.0$ Lyman-$\alpha$ and Lyman-$\beta$ transmission
• Discovery of the most metal-poor damped Lyman-alpha system
• A deep search for metals near redshift 7: the line-of-sight towards ULAS J1120+0641
• Deconvolving the Wedge: Maximum-Likelihood Power Spectra via Spherical-Wave Visibility Modeling
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